Fluorescent screen



April 7, 1925. 1,532,796

F. BALCH FLUORESCENT SCREEN Filed Jn. 1o, 1925 FI L 4 5 2 mmwwmmmmmmmINVENTOR ard@ aZaz, BY@

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Patented Apr. 7, 1925.

' PATENT OFFICE.

FRANK BALCH, QF SALEM, MASSACHUSETTS.

FLUORESCENT SCREEN.

Application filed January 10, 1923. Serial No. 611,872.

To all whom t may concern.'

Be it known that I, FRANK BALCH, a citizen of the United States ofAmerica, residing at Salem, in the county of Essex and State ofMassachusetts, have invented certain new and useful Improvements inFluorescent Screens, of which the following is a full, clear, and exactspecification.

This invention relates to uorescent screens used to intensify the imageproduced on a sensitive plate or film by X- rays. The active layer of afluorescent screen generally consists of fine particles of fluorescentmaterial, usually a salt in crystalline form held in suspension in abinding material. I have found that this binding material can comprisecellulose acetate as its principal ingredient, and that a screen can bemade of high intensifying value which is not fragile, which isnoticeably free from mechanical imperfections and which may be made bysimple and reliable methods of manufacture.

Reference will now be made to the accompanying drawing in which the samereference characters designate the same parts throughout:

Fig. 1 is an enlarged fragmentary section of the film screen on thesupporting table;

Fig. 2 is a perspective View of a com'- plete screen being strippedvfrom the table.

In manufacturing the preferred form of my improved screen I form anemulsion able binder. f

A solution is first made in accordance with the following formula:

When this is thoroughly mixed and the crystals dissolved there is addedthereto, cellulose acetate, dry, 680 grams. When or mixture of celluloseacetate and asuitfully `dissolved, this is strained. This solution willbe hereinafter referred to as solution A. I f it is necessary ordesirable to thin it the following thinning solutionv may be used:acetylene tetrachloride 1000 cc., methyl alcohol 125 cc.

I then prepare the following mixture:

Mixture B.

Calcium tungstate 4550 grams. Acetylene tetrachloride 500 ce. Methylalcohol 15 cc. Castor oil cc. Canada balsam 15 cc.

This is ground in a pebble mill to a very fine mass and strained. All ofthe constituents of both formulaeJ are referably of 'a high degree ofpurity. I t en mix the total amount of mixture B given in the formulawith about 1800 cc. of solution A and remove all air bells by means ofproper suction with an air pump. This is poured at room temperature overa polished glass table l and forms a layer 2 which dries slowly by thepartial evaporation of the solvents, forming a smooth film which, whilecoherent, is rather fragile for constant or rough usage. I form abacking or supporting layer 3 by pouring over this film while stillsomewhat tacky a coating of solution A, the amount depending on thethickness of the desired support 3. p

It is sometimes `desirable to attach to a lm screen' 4, made asdescribed, a further back or support, and I use preferably a piece ofcardboard 5 glued to the film screenv 4' just described. This may beattached before or after stripping the :61m screen from the glass plate1, but I prefer to do so' before stripping. Pieces' of cardboard are cutto the desired dimensions and the screen material on the glass plate iscut to sizes slightly larger than the pleces of cardboard. A piece ofcardboard 5 is I then glued to the corresponding ilm screen section,being located so as to leave a narrow margin 6 of the lm screen aroundthe cardboard. I find that the glue adheres to the cellulosic supportmuch more firmly if the latter is, when dry, first evenly coated with athin even film of bleached shellac dissolved in alcohol. of equivalentsis possible in the adhesive composition used, and the following is givenas a typlcal satisfactory formula: v-

Liquid ish glue 32,0 cc. Thick syrup of sugar 160 cc. Glycerin 10 cc.

of example this proportion is about 5% but- I do not limit myself tothat figure, but if too great a percentage, which I place at 8 per cent,be used, the efficiency of th screen becomes noticeably less. In afinishe screen cellulose acetate appears to be more transparent tofluorescent rays than' some other binding materials and aiiordsrothermanufacturing advantages. i Y

I have found that satisfactory results are obtained if the filmcontaining the luorefscent salt has a thickness of about .015 vand thesecond or supporting iilmKhas a thickness of about .035. I do not,however, limit myself to these dimensions which are given only by way ofexample. The thickness of the cardboard is quite immaterial. j

While I have herein' fully described the preferred embodiment, it is tobe understood that yI contemplate as Within my invention suchmodifications and equivalents as fall withinv the terms of the appendedclaims.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A iuorescent screen having an active A i very wide rangef layercomprising a mixture of fluorescent material and a binder, thebindercompris# ing cellulose acetate.

2. A iiuorescent screen having an active layer comprising a mixture offluorescent material and a binder, the binder comprising celluloseacetate andy /acetylene tetra'- chloride.

3. A iuorescent screen having an active layer comprising a mixture ofuorescent material and a binder, the, binder comprising celluloseacetate, and the proportion of the cellulose acetate/td the uorescentmaterial being not over eight per cent by weight.

4. A {iuorescent screen having an active layer comprising a mixture 'offluorescent material and a binder containing cellulose acetate and asecond layer adherent thereto and comprising a cellulose ester.

5. A fluorescent screen having an active layer comprising a mixture offluorescent material and a binder containingv cellulose acetate andacetylene tetrachloride, and a supporting, backing layer adherentthereto and thicker and stronger than said active layer.

6. A fluorescent screen having an active layer comprising a mixture ofiuorescent material and a binder containin cellulose acetate, .theproportion of the cel ulose acel tate to the iuorescent material being.not over eight per cent by .weight and a supporting, backing layeradherent vthereto and Ithicker-and stronger than said activelayer,

and comprising a cellulose ester.

y, 7 A iuorescent screen having an active layer comprismg a mixture ofliuorescent material and a binder containing lcellulose acetate, andacetylene tetrachloride, the proportion of the cellulose acetate to thefluorescent'material being not over eight per cent by weight and asupporting, backing layer adherent thereto and thicker and stron er thansaid active layer, and vcomprising cel u- `lose acetate.

Signed at Salem, Massachusetts this 5th day lof January 1923.-

FRANK BALCH,

